Coagulant for synthetic rubber latices



Patented June 19, 1945 Charles F. Fryling, Akron, Ohio, assignor to TheB. F. Goodrich Company, New York, N. Y., a corporation of New York NoDrawing. Application July 30, 1941, Serial No. 404,659

. 10 Claims.

This invention relates to the coagulation of synthetic rubber latices,and particularly to the use of a specific kind of a coagulant whichdeposits the synthetic rubber in a form which expedites furtheroperations such as washing-and drying.

It is well known that by the polymerization in the form of an aqueousemulsion of a butadiene either alone or in the presence of monomerscopolymerizable therewith stable dispersions may be obtained. In amajority of cases, the synthetic rubber latex is coagulated, washed, anddried to form a massive product which may be further treated in much thesame manner as natural rubber. I

If common plantation practice is applied to the coagulation of syntheticrubber latex rather than natural rubber latex, the product obtained isin theform of a coherent mass. Thus if acid in dilute solution is addedto a synthetic rubber latex containing soap as the emulsifying agent,the coagulum coheres upon standing into an amorphous body which can belifted from the water during an" acid coagulation breaks up the coagulumto a certain extent, but the particles are sticky and readily coherewhen the stirring is stopped. It is an object of this invention toprovide a coagulant which will precipitate synthetic rubber from anaqueous. dispersion in the form of discrete' particles which have littletendency to cohere. It is a further object of this invention to providea coagulant which effects complete coagulation in a short space of time.

I have found that these and-other objects may be accomplished byemploying as the coagulant a water-soluble aluminum salt. Aluminumsulfate, an inexpensive and readily available salt, is the preferredmaterial, althougli bther water-soluble aluminum salts such as aluminumchloride, aluminum' nitrate, and aluminum acetate may be employed ifdesired. Double aluminum salts which ionize to yield aluminum ions suchas, po-

tassium aluminum sulfate, sodium aluminum-..

chloride, etc., may also be employed.

The use of aluminum salts is particularly-ade vantageous when thesynthetic rubber latex contains as the emulsifying agent a water-solublesoap such as sodium oleate, potassium palmitate, sodium myristate,sodium laurate, or other alkali metal salts of higher fatty acids whichform insoluble soaps with aluminum. In this case, coagulation with analuminum salt is believed to be mainly due to destruction of the'emulsifying agent through the formation of the insoluble aluminum soap.The use of at least excess of aluminum salt over that theoreticallyrequired to react with the soap is desirable to insure rapid andcomplete coagulation. Aluminum salts are alsoextremely useful coagulantsfor synthetic rubberlatices containing synthetic saponaceous emulsifyingagents such as hymolal sulfates and aryl sulfonates of the typerepresented by sodium lauryl sulfate and sodium isopropyl naphthalenesulfonate. The coagulation of synthetic latices containingnonelectrolytic emulsifying agents such as gelatin, albumen, andaromatic compounds rendered soluble by the presence of a chain of groupsterminating with a, hydroxyl group may also be effected by thecoagulants herein described, although considerably larger amounts ofsalt must be employed than where the coagulation is effected pricipallyby formation of an insoluble aluminumsoap.

Although coagulation occurs when the coagulant is added in solid form,in commercial opera tions the aluminum salt is ordinarily mixed with rthe latex in the form of an aqueous solution. A

1% to 10% solution of A12(SO4) 3.18H2O in water is very satisfactory,although the concentration is in no way critical. Any of the ordinarymethods .of coagulation may be employed when an aluminum salt is such asthe coagulant. The synthetic rubber latex and the solution of aluminumsalt may be brought together in avcoagulating nozzle such as thatdescribed in the copendingapplication of Waldo L. Semon, Serial No.367,821, filed November 29, 1940, in which turbulent intermingling ofthe streams is efiected. If desired, the latex may be run in a smallstream into an aqueous solution of aluminum salt being stirredsuiiiciently to secure deposition of the coagulum in the form of crumbsof the desired size. Alternatively, the coagulant may be run into thelatex. This alternative is not preferred, however, since a coagulum ofsomewhat larger particle size which is consequently more diilicult towash is obtained.

As a specific example of a preferred method of coagulatinga syntheticrubber latex with an that about a ton of coagulum was formed in an hour.The coagulating bath was stirred throughout the addition of thesynthetic rubber latex to maintain a moving liquid surface upon whichthe latex could drop, thereby preventing the latex from falling onpartially coagulated rubber and forming lumps. During the last part ofthe addition, the bath thickened somewhat, so steam was admitted beneaththe surface of the bath to assist in the agitation and to heat the bathto about 60 C. The coagulum was in the form offine crumbs which did notcohere when the stirring was stopped and which did not adhere to thestirrer or the walls 01' the vat during the coagulation. The desirablecharacteristics peared to be due to the fact that an aluminum salt wasused, for coagulation with water-soluble of the coagulum apsalts orother polyvalent metals such as zinc and lead produced coagula similarto those obtained with an acid coagulant which cohered and weredifllcult to wash and dry.

The same desirable results are obtained by coagulating synthetic rubberlatices formed by the emulsion polymerization of other butadienes- 1,3such as isoprene, piperylene, 2,3-dimethylbutadiene, chloroprene, orother homologues or analogues of butadiene-L3 polymerization reactionsin essentially the same manner, either alone or in admixture with eachother and/or other monomers copolymerizable therewith such as styrene,isobutylene, acrylonitrile, methyl methacrylate, methyl acrylate, methylvinyl ether, other unsaturated and ketones.

Although I have herein disclosed a specific embodiment of my invention,I do not intend to limit the invention solely thereto for it will beobvious to those skilled in the art that other coagulating proceduresmay be employed without departing from the spirit and scope of theinvention as defined in the appended claims.

I claim:

. 1. The method of coagulating a stable aqueous polymer dispersionprepared by the polymerizahydrocarbons, esters, ethers,

tion in aqueous emulsion of a polymerizable material consistingpredominately 01' a 'butadiene- 1,3, which comprises mixing awater-soluble aluminum salt with said dispersion whereby coagulation ofthe dispersion is effected and discrete, substantially non-coherentparticles of rubbery polymer are formed. p

2. The method of coagulating a stable aqueous polymer dispersionprepared by the polymerization in aqueous emulsion terial consistingpredominately of butadiene- 1,3, which comprises mixing a water-solublealuminum salt with said dispersion whereby coagulation of the dispersionis effected and diswhich enter into methyl vinyl ketone, and

of a polymerizable macrete, substantially non-coherent particles ofrubbery polymer are formed.

3. The method of coagulating a stable aqueous polymer dispersionprepared by the polymerlzation in aqueous emulsion of a mixture ofbutadiene+1,3 and a lesser amount of a monomer copolymerizable therewithin aqueous emulsion, which comprises mixing a water-soluble aluminumsalt with said dispersion whereby coagulation of the dispersion iseffected and discrete, substantially non-coherent particles of rubberymaterial are formed.

4. The method of coagulating a stable aqueous polymer dispersionprepared by the polymerization in aqueous emulsion of a mixture ofbutadiene-1,3 and a lesser amount of a monomer copolymerizable therewithin aqueous emulsion, which comprises mixing an aqueous solution of awater-soluble aluminum salt with said dispersion whereby coagulation ofthe dispersion is effected and discrete, substantially non-coherentparticles of rubbery material are formed.

5. The method of claim 4 wherein the aluminum salt is aluminum sulfate.6. The method of claim 4 wherein the dispersion is prepared by-thepolymerization in aqueous emulsion of a mixture of butadiene-LB and alesser amount of acrylonitrile.

7. The method of claim 4 wherein the dispersion is prepared by thepolymerization in aqueous emulsion of a-mixture of butadiene-1,3 and alesser amount of styrene.

8. The method of coagulating a stable aqueous polymer dispersionprepared by the polymerization in aqueous emulsion of a mixture ofbutadiene-1,3 and a lesser amount of a monomer copolymerizable therewithin aqueous emulsion in the presence of a water-soluble soap as theemulsifying agent, which comprises mixing said dispersion with anaqueous solution of an aluminum salt whereby coagulation of thedispersion isaefiected and discrete, substantially non-coherentparticles of rubbery material are formed.

9. The method of claim 8 wherein the dispersion is prepared by thepolymerization in aqueous emulsion of a mixture of butadiene-1,3 and alesser amount of acrylonitrile; and the aluminum salt is aluminumsulfate.

10. The method of coagulating a stable aqueous polymer dispersionprepared by the polymerization in aqueous emulsion of a mixture ofbutadiene-1,3 and a lesser amount of a monomer copolymerizable therewithin aqueous emulsion, which comprises adding said dispersion to anaqueous solution of a water-soluble aluminum salt and stirring thesolution during the addition whereby coagulation of the dispersion iseffected and discrete, substantially non-coherent crumbs of rubberymaterial are formed.

' CHARLES F. FRYLING.

